There is a great demand from various industries for better thin-film coatings to protect material surfaces from corrosive and abrasive agents. Although many types of thin-films are available, each suffers from certain undesirable defects that are largely contributed by the lack of durability and ineffectiveness of the coatings. The effectiveness of a protective coating depends on both the chemical and mechanical properties of the film; whereas, the durability of the coating is governed by the interfacial adhesion between the film and the substrate as well as the wearcorrosion resistivity of the film.
The methods commonly used to prepare thin-films are generally of either chemical or physical techniques. One of the most utilized chemical methods for the production of protective or decorative films is by electrolytic deposition which provides a means of depositing metal films from an ionic solution of metal onto a metallic substrate. Anodization, a particular kind of electrolysis, makes use of the aluminum surface as the anode which during electrolysis is being oxidized by reacting with water in the electrolyte to form a nonporous coating of hydrated aluminum oxide thereon. However, the utility of this process is limited to only a few metals and it has been widely used for the production of tantalum oxide and aluminum oxide barrier films. Also, the brittle nature of the thicker film makes them susceptible to corrosion fatigue which causes local stress cracking and eventual rupture of the films. Other chemical methods include various organic coatings and they are an economically attractive choice for corrosion protection since they are easily handled and applied. Unfortunately, the lifetime of organic coatings is short due to their permeability to corrosive gases.
Physical methods consist of thermal and electron beam evaporation, and sputter deposition. These methods can produce more pure and well defined films, but the application of these films often requires an expensive vacuum apparatus or a particle-free environment.
In recent years, much attention has been given to utilize organometallic compounds for thin-film deposition because practically any organometallic compounds can be synthesized from a wide variety of elements in the periodic table. In addition, the abundant choice of commercially available organometallic compounds and the establishment of many chemical reactions for them have generated much enthusiasm for the development of new coating materials and techniques to meet the increasing demands of an industrial society. However, none of the thin-film processes in use today is satisfactory; they all suffer from one or more drawbacks such as control difficulty, process complexity and substrate damage. The invention described herein provides a simple and low cost process for producing unique and high quality protective coatings that have overcome most, if not all, limitations of existing coatings.